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Gulf of Mexico Brine Pools with Megan Cook

August 19, 2013

Megan Cook Photo (c) Ocean Exploration Trust

Have you ever met a little kid who refuses to go to bed, because they know the minute they lay their head down, something amazing and unexpected will happen? No matter how strong the onset of the Sleepies, this child will valiantly fight them back until wee-hours just to ensure the impending night’s biggest excitement won’t slip by. Over the last few weeks out at sea, I’ve been the adult-reincarnate of that child!

Aboard the E/V Nautilus we are exploring the Gulf of Mexico seafloor using deep diving ROVs around the clock 24 hours a day. Capable of diving to 13,000 feet, mapping the seafloor and bringing up a suite of water, sediment, chemical, or biologic samples the vehicles can produce never-ending possibilities for what lies just beyond the edge of the ROV lights.

Hercules ROV (c) The Ocean Exploration Trust

After my watch I would linger, unwilling to step away from our own live deep sea TV. And without fail the Sleepies would attack each night. Tucking myself into my bunk I would quietly conceit one more victory to heavy eyelids and slip off to bed to recharge for another day of exploration.

But last week I woke to learn my inner four-year-old’s instincts had been right: Never go to bed! No sooner than I sat down at breakfast I heard, “How INCREDIBLE was the brine pool we found last night?!”

As I slept the team discovered an underwater pond, a lake on the seafloor!

Brine water is four or five times saltier than seawater and this lake had its own shoreline and surface. The lake stretched 30m long (longer than a basketball court) and was estimated 5m deep. A raised bank of salts formed the shoreline with live mussel beds growing up the outer slopes. A thin margin ringed the slope crest clearly defining the closest boundary for living creatures. The super-high salinity of brine water makes it uninhabitable for nearly all species of life. Only a few species of archaea, single- celled extremophiles, can tolerate these conditions. Fish glided above the pool, but never sank into the brine. One particular deep sea isopod must have crept a little too close to the edge. We found him tumbled in head first, dead half sticking from the brine.

Isopod – (c) The Ocean Exploration Trust

This expedition was focused on looking at methane seeps on the seafloor. At these sites small bubbles of natural gas gurgle from the seafloor, like carbonation in a can of soda. Methane seeps support a rich diversity of chemosynthetic organisms; we had been sampling them for more than a week. Multibeam mapping data traced a bubble plume to 4,200 feet here. After the investigation during my watch proved fruitless our charts were labeled ‘the pit of despair’. We had only been a few dozen meters from this brine pool without knowing it! On the return visit, the team not only happened on a brine pool, but found the missing methane seep rising from the center of the bizarre lake. The bubbling from the lake’s surface forced some seawater to mix creating a turbid haze over the lake. Replaying the video, the cloudy boundary looks like a witch’s cauldron. This site was cleverly designated ‘the JACUZZI of despair’.

Brine pools are found around the world, and are well-documented in the Gulf of Mexico. The thrill of exploration is palpable on the E/V Nautilus as we were the first to identify and document this brine pool! Brine forms as water intrudes into deep buried salt plates dissolving some of their minerals. Warping and cracking of salt plates allows more water into the seafloor, pushing out the brine. When brine flows into a divot or basin, a brine pool will form. Our Jacuzzi-of-Despair even had a low edge where brine flowed down the bank like an over-filled bathtub.

The Jacuzzi of Despair – (c) The Ocean Exploration Trust

The salts inside the heavy brine make the water very dense and heavy. This prevents brine from mixing well with the water above effectively creating a smooth lake surface. Eager to sample the brine for our science team, we dunked the ROV Hercules. Disturbance waves swept across the lake surface just like ripples on a puddle. Because Hercules was weighted to work neutrally buoyant in seawater, it was incredibly difficult to sink the vehicle in this heavy brine. The manned submersible Alvin once settled entirely on top of a brine pool. Even 36,000 pounds of weight balanced for neutral buoyancy couldn’t sink into the haze. Eager for a sample, our team mounted a Niskin water sampling bottle underneath Hercules. Still, we needed to drive down with the thrusters to sink below the brine/seawater boundary. Waves of brine washed over the shore edge as Hercules dunked.

Hercules submerges into brine pool (c) The Ocean Exploration Trust

With my jaw on the breakfast table, I was kicking myself for closing my eyes the night before. In an act of good karma the science team’s plans brought us back to our brine pool once more to share the views. As the Hercules lights brushed the edge of the pool, I knew it was one of the most surreal oceanscapes I’ve had the pleasure to witness. I felt like detecting our pool was finding a needle in a needle stack although I was addicted to believing another could be awaiting discovery constantly just beyond the lights. With more than 95% of our seafloor unmapped and unexplored, we have many more incredible seascapes waiting for our cameras and researchers.

I am continuously inspired by the team’s discoveries in the deep sea and immensely grateful for the Ocean Exploration Trust’s commitment to sharing discovery globally. Although I was asleep, audiences were watching live over the internet at home, on their smart phones, and in their classrooms as our Jacuzzi of despair lit up for the first time. Teleprescence brought this story to nearly twenty museum audiences within hours of its discovery. I hope more ocean lovers will take advantage of the chance to explore deeper as OET continues their exploration season through November.

Mussels on the edge – (c) Ocean Exploration Trust

The Ocean Exploration Trust is committed to working with the highest quality researchers to use cutting edge technology to go places on the seafloor no one has ever been before and inspire a generation of future-explorers to pursue STEM careers. Exploration streams live 24/7 on www.NautilusLIve.org. Be sure to check out the highlight videos and photo albums for more from the brine pool!